This invention relates to multicylinder internal combustion engines and particularly to such engines having provision for protecting the rotating system formed by a crankshaft and a flywheel from stress otherwise induced by torsional vibration.
It has long been recognized that the crankshaft and flywheel of a multicylinder internal combustion engine form a rotating system which has, because of the moments of inertia and coupling of the components, a natural or resonant frequency of torsional vibration. The pulsating forces applied to a crankshaft as a result of the firing of the cylinders of an engine give rise to such vibration and will, at certain rotational speeds, impose stress which will cause a crankshaft or the bearings supporting the crankshaft to fail.
As is indicated in an important reference in the field of this invention (S.A.E. Paper SP-445 presented by Robert C. Bremer, Jr. at the West Coast International Meeting in Portland, Oregon, Aug. 6-9, 1979), the usual approach in dealing with torsional vibration and stress in the environment of this invention is to analyze a crankshaft/flywheel system as if it were a simple torsional oscillator. In one approach to such an analysis, the movements of inertia of the components are resolved about the crankpin closest to the flywheel and the system is treated as if the pin were a spring connecting the portion of the crankshaft forward of the pin with the flywheel. The system may then be viewed as two masses (the crankshaft and the flywheel) joined by a springy connector (the pin) which has a torsional spring rate which determines the natural frequency of torsional vibration of the system. The system may then be analyzed for harmonic frequencies which fall into the operating range of the engine (in revolutions per minute) or which combine with other frequencies in such a way as to generate stress and possibly become destructive. As such frequencies are found, dampers are designed for mounting on the end of the crankshaft remote from the flywheel for the purpose of damping out or reducing the vibration by dissipating energy.
While such an approach has achieved some success, as evidenced by the commercially produced engines and vehicles which employ this technology, significant difficulty has been encountered in attempting to apply the technology to engines which have a wide range of operating speeds, and therefore encounter a wider range of possibly dangerous operating conditions.